DO NOW: Write down 2 ways something can grow. (1min) DO NOW: Write down 2 ways something can grow. AIM: Reproduction at the Cellular level- Cell Division What is Mitosis? What is Meiosis?

How do cells grow? Cells can grow in two ways: Cells can grow by increasing in size, (getting larger) Cell can also grow by increasing their number, (dividing – Mitosis)

What is Mitosis? Mitosis is a type of cell division where a cell reproduces itself by splitting to form two new identical cells (clones). Mitosis produces new cells from an original old one. This is how organisms grow and replace dead or damaged cells.

What types of cells do mitosis? Single cell organisms use mitosis to reproduce. Ameba, bacteria and algae. Body cells are any cell in the body EXCEPT sperm and egg cells. Skin cells, muscle cells, nerve cells and ect. Cells AFTER the zygote is formed.

The steps of Mitosis (step 1) 1) The first step in mitosis is that cell must prepare itself to divide. It must start doubling all its organelles. (mitochondria, ribosome, chloroplast (plants)) In the nucleus, the DNA which is spread out in long strings begin to condense (coil) to form chromosomes. In humans there are 46 chromosomes. The DNA contains all the genes to make the entire organism.

The steps of Mitosis (step 2) 2) The chromosomes (DNA) begin to duplicate forming an “X” like shape.

The steps of Mitosis (step 3) 3) Now that the chromosomes are doubled, they begin to line up in the middle of the cell.

The steps of Mitosis (step 4) Small fibers attached to the center of each chromosomes begin to pull the “X” shaped chromosomes apart and toward each end of the cell.

The steps of Mitosis (step 5) Membranes form around the newly separated chromosomes and the cell begins to pinch at the middle.

The steps of Mitosis (step 6) Finally a membrane forms at the “pinch” and two cells are formed. The DNA unwinds itself.

Mitosis and Asexual Reproduction In multicellular organisms, mitosis is a way to make more cells. Mitosis occurs in all body cells. In many unicellular (single cell) organisms, mitosis is the way they reproduce. Using mitosis as a means of reproducing is a form of asexual (one parent) reproduction. Each offspring is a clone and contains exactly the same genetic information.

Examples of Asexual Reproduction Each offspring is identical to the parent

What is Meiosis? Meiosis is another type of cell division. Instead of two identical cells in respect to the parent, the new cell(s) will have half the number of chromosomes. Meiosis ONLY occurs in the sex cells- Sperm and Egg cells.

Meiosis only occurs in the sex organs (testes in males, ovaries in females) Sex cells are called Gametes

Why do the daughter cells have half the chromosomes? The purpose of the sex cell in meiosis is to be able to combine with another sex cell to form a new cell “zygote”. By having only half the number of chromosomes, the union of the two sex cells will result in a zygote containing the right number of chromosomes ( ½ + ½ = whole)- one set of chromosome from the sperm and one set from the egg. Human cells have 46 chromosomes or 23 pairs, therefore human gamete cell have____ non paired chromosomes. Because 2 gametes are needed to make an offspring, this form of reproduction is called sexual reproduction. 23

46 46 Mitosis Cell Division 46 46 46 46 Meiosis Cell Division 23 23 23 23

92 46 46 46 Sperm Egg

46 23 23 23 Sperm Egg One set of chromosomes come from the father and some come from the mother

Steps of Meiosis The first part of Meiosis follows the same steps as in Mitosis, except instead of the DNA uncoiling when the cells splits, the cell splits a second time. This leaves the gamete cells without a chromosome pairs.

Fertilization: The meeting of the Gametes A zygote is a fertilized egg. Once the zygote is formed, the new cell will have some of the DNA from the sperm and some from the egg. This means that the zygote contain some genes from the father and some genes from the mother. For this reason, the developing embryo will have traits (characteristics) of both the mother and the father.

How can I remember which cell division is which? I use mitosis to make my own cells My parents used Meiosis to make me.

Fertilization: The meeting of the Gametes (continued) Because meiosis creates cells with only 23 non-paired chromosomes, when two gametes meet (fertilization) the new cell (zygote) will have the proper number of chromosomes (23 pair or 46 total). As a results of the gametes combining, the offspring will have characteristics (inherit features) from both parents.

Fertilization: The meeting of the Gametes In a normal human cell, the nucleus contains 23 pairs of chromosomes (a set of 23 chromosomes from the mother and a set of 23 chromosomes from the father or a total of 46 chromosomes) Each of the 23 chromosomes are different from each other and they are labeled 1 through 23. When the chromosomes are paired (example: mother’s chromosome 5 & father’s chromosome 5), they are said to be homologous (same)